A variety of methods have been developed for the synthesis of .alpha.-alkylated .alpha.-amino acids. Many of these methods involve the use of chiral auxiliaries or multiple step reaction sequences (Schollkopf, Angew. Chem. Int. Ed. Engl. 2 117 (1978); Schollkopf, Syntheis 271 (1984); Schollkopf, Liebigs Ann. Chem. 399 (1987); Seebach, Helv. Chim. Acta 68 1243 (1985); Belokon, J. Chem. Soc., Chem. Commun. 171 (1985); Ihara, J. Org. Chem. 54 5413 (1989); Ojima, Tetrahedron 5307 (1988); Fitzi, Tetrahedron 44 5277 (1988); Fadel, Tet. Lett. 28 2243 (1987)). One method involves the enzymatic resolution of a racemic .alpha.-alkylated .alpha.-amino acid (Kruizinga, J. Org. Chem. 53 1826 (1988). Some of the methods cited involve reaction conditions which are not compatible with functional groups that would be desirable to introduce in the side chain of an .alpha.-alkylated .alpha.-amino acid. Furthermore, some of the methods cited do not produce .alpha.-alkylated .alpha.-amino acids in high optical purity.
As a result, there is a continuing need for methods that are simple, use inexpensive reagents and produce .alpha.-alkylated .alpha.-amino acid products in good yield and high optical purity.